This invention pertains to a coaxial valve including a valve box, having at least one fluid inlet opening, at least one fluid outlet opening, and a common flow channel connecting the fluid inlet and fluid outlet openings together. A tubular shaped valve casing, which is prevented from turning but permitted to be axially pivotable, features a fluid inlet port and an outlet port, which join inside the common flow channel. A shutoff mechanism, located inside of the valve box, is coaxial to the valve casing and designed to shut off the fluid inlet port or the outlet port of the valve casing, and a drive is provided to produce axial movement of the valve casing. The valve may be used with cryogenic fluids.
Special requirements must be met with valves that serve for the regulating and sealing off of a liquid or gaseous medium under extreme conditions, such as chemical aggressiveness, very high or very low temperatures, or very high pressure. Fields of application for valves that serve to seal off a fluid or gaseous medium are found in power trains in air and space travel. These valves are exposed to extreme temperatures and extreme temperature changes. For valves used for fluid and gaseous rocket fuels, there are additional parameters which increase certain demands on this type of valve, such as demands relating to mass flow, high pressure, and short switching time for opening and closing of the valve or for getting the valve into a special position.
A valve with these specifications is known from German document DE 199 60 330 C2. The valve shaft of this valve is moved axially in relation to the valve closing mechanism within the flow by a lever which is activated by an electric servo motor from the outside of the valve body.
Since this servo motor is mounted externally, this valve has relatively large mounting dimensions. In addition, operation using a lever mechanism is complicated and therefore presents increased risks for malfunctioning to an extent which is unacceptable in applications in space aviation.
It is one object of this invention to design a valve with these specifications which is extremely reliable in its operation because of its compact construction, low friction, low energy requirements, and light weight.
This object is achieved by way of a valve in which the valve casing is provided, at least in sections, with at least one threaded external nut at an outer circular groove, in which the valve casing is enclosed by a coaxial drive casing at a location of the outer circular groove, in which the drive casing is provided with at least one threaded inner circular groove adapted to the outer circular groove so that ball bearings running along the inner and outer circular grooves create tension against one another, thus forming a ball planetary gear of a ball rotary spindle drive, and in which the drive casing is located inside of the valve box, is pivotable but firmly seated axially, and is made to pivot by a drive motor inside of the valve box.
The valve shaft is therefore equipped, section by section, on its outer surface with at least one external adjusting nut with threads and surrounded in each section of this external adjusting nut by a drive sleeve which is coaxial to the valve shaft. The drive sleeve is equipped on its interior with at least one threaded internal adjusting nut, which fits against the outer adjusting nut in such a way that the inner and outer threads match and thus perform the ball screw-driven propulsion of a linear integrated ball screw drive. The drive shaft can turn within the valve casing but is axially secured and rotated by a driving motor installed on the inside of the valve shaft. The driving motor and the driving shaft actuate the drive for the valve shaft by taking into consideration the section of the threaded outer nut and the bearings which are integrated into the valve shaft.
The valve shaft is thus identical with the spindle of the screw-driven propulsion. The advantage of the construction described is the compact structure of this coaxial valve which is achieved by the integration of the valve shaft with the screw driven propulsion, and the resulting light weight.
Further advantages of this invention will also be apparent.
It is especially of advantage when the drive casing is surrounded by the rotor of the drive shaft and is connected to prevent any rotation. Configuring the motor coaxially with the valve shaft provides for a particularly compact construction of the coaxial valve. It is advantageous that the rotor is surrounded by a stator from the driving motor and that the stator is prevented from turning within the valve casing.
It is also beneficial when the stator's position allows for at least a certain amount of axial shifting because this design will compensate for thermal expansion of the various elements of the drive.
In another advantageous design the rotor can turn inside the stator by means of at least two radial roller bearings. The provision of this roller bearing ensures that the space between the rotor and the stator remains constant during operation, especially under temperature fluctuations.
An electrically driven driving motor presents an advantage. It is also conceivable that, for example, a hydraulic driving motor could be used.
In another advantageous embodiment, the drive shaft is positioned above two axial roller bearings. This placement promotes the attachment of the drive shaft within the valve casing and thus ensures a definite axial positioning of the ball screw driven propulsion.
Optimally, the two axial roller bearings are each provided with a circular, domed convex outer surface within their respective outer bearing rings. These convex outer surfaces are supported in turn by a corresponding concave inner surface on the interior of the valve casing where the respective spherical and concave and convex surfaces share the same central point on the axis of the valve casing. With this design, the entire drive system, including the ball screw propulsion, is at least to some degree pivotable in all directions around the central point, so that tensions caused in the drive, especially by temperature fluctuations, are counter-balanced in the casing and/or in the drive. As a result, a secure valve seal is guaranteed, and an abrasion-free operation of the valve shaft is enabled even in the presence of tension within the valve casing and/or in the drive.
These features are improved, in an enhanced modification of the invention, by providing the closing mechanism with a first part which has a domed concave surface pointing toward the valve shaft, and by having a domed convex surface of a second part which can be pivoted in such a way that these two parts are connected in an axial direction, but can move relative to each other along the domed surfaces, while the central point of the domed surfaces of the closing mechanism is aligned with the central point of the two domed axial roller bearings. In this way, the second part of the closing mechanism with a tight seal is positioned in a way that allows for pivoting around the same central point, thereby further improving the reliability of the seal even where there is tension within the valve casing and/or in the drive.
In a preferred embodiment, the closing mechanism is equipped on the second part with a valve seat which, together with the front-sided rim around the valve port of the neighboring end of the valve shaft, effects an even better seal when the valve is closed.
The invention will now be described by way of an example shown in the drawings.